Disclosed herein are novel photoacid generator compounds polymerizable into a photoresist polymer, and a photoresist composition which includes the polymerizable photoacid generator.
Chemical compounds which decompose to generate acids when exposed to radiation in the ultraviolet region of the spectrum (i.e., <300 nm), also known as photoacid generators, are the basis for “chemically amplified” deprotection or crosslinking of polymers in chemically amplified photoresists for microelectronics applications. Outgas sing of the decomposition products of such materials, however, can coat and corrode the optics of the exposure tools for such photoresists, where the optics may only be millimeters away from the photoresist being exposed.
While measures to limit the damaging effects of outgas sing by for example, cleaning the optics and/or including sacrificial barriers or filters have been used for earlier generation lithographic tools (operating at 248 nm and 193 nm) and using refractive optics, the industry trend toward increased resolution at smaller and smaller linewidths of less than 45 nm, and the development of new tools operating at significantly shorter wavelengths (such as in the extreme ultraviolet (EUV) region at 13.5 nm) and which use advanced reflective optics, may not be compatible with such strategies. There is therefore interest that control of outgassing should occur at the compositional level in a photoresist. In addition, control of linewidth roughness is required in advanced photoresists for use at EUV wavelengths, which correlates to the diffusability of the components of the photoresist.
European Patent No. 2 020 616 A2 discloses photoacid generators having useful outgassing characteristics, when used with a phenolic polymer having vinyl-ether derived protecting groups. The photoacid generators are based on a sulfonium cation having an aryl group connected to the sulfonium center preferably incorporating at least one hydroxy group, and a bisaryl group with each aryl commonly connected to the sulfonium center. While the photoacid generators disclosed in this reference show improved outgassing relative to, for example, triphenylsulfonium cation-based photoacid generators, the examples (particularly Examples 1 and 9) show that improvements in outgassing obtained with these photoacid generators may also compromise the linewidth roughness.